Roux was Duclaux’s protégé and assistant, Duclaux suggesting that Pasteur take him on. He became a close collaborator with Pasteur, working with him on avian cholera, anthrax and rabies (they developed a vaccine). Chamberland and he worked together; when Pasteur was awarded the Légion d’Honneur, he insisted Roux and Chamberland be honoured too. He helped Mechnikov with his work on syphilis (they succeeded in passing the infection to apes), and became his very close friend. Roux was joined by Yersin in his work on diphtheria, and succeeded Duclaux as director on the Pasteur Institute.